WJEC AS Mineral Guide

I.G.Kenyon

Quartz (silicate)

1cm

Quartz (variety citrine)

Hardness 7, not scratched by steel

No cleavage but shows conchoidal fracture

Hexagonal crystals terminated by pyramids

Rose quartz showing conchoidal fracture

5mm

Orthoclase Feldspar (silicate)Hardness 6, barely scratched by steel

2 cleavages intersecting at 90° results in blocky shape

Commonly flesh coloured

Crystals show simple twinning

2cm

Plagioclase Feldspar (silicate)Hardness 6, barely scratched by steel

2 sets of cleavages intersecting at 90°

resulting in blocky form

Commonly creamy white or grey in colour

Crystals show multiple or repeated twins

1cm

Biotite Mica (silicate)

Hardness 2.5-3.0 scratched by a

copper coin

Shows perfect basal (parallel)

cleavage

Has a distinct pearly lustre

Brown or black in colour 2cm

Muscovite Mica (silicate)

Hardness 2.5-3.0 scratched by a

copper coin

Shows perfect basal (parallel) cleavage

Has a distinct pearly lustre

Whitish, straw or silvery in colour

2cm

Hornblende (amphibole/silicate)

Hardness 5.0-6.0, just scratched by steel

2 sets of cleavages intersecting at 60°/120°

Greenish black in colour

1cm

Augite (pyroxene/silicate)

Hardness 5.0-6.0, just scratched by steel

2 sets of cleavages intersecting at 90°

Greenish black in colour

Olivine (silicate)

Hardness 6.0-7.0, not scratched

by steel

Olive green in colour

No cleavageOlivine, Canary Islands

2cm

Andalusite/Chiastolite (silicate)

Hardness 6.5-7.5, not scratched by steel

Occurs as needle-like crystals but square in

cross-section

Crystals have dark inclusions in the centre,

like lead in a pencil1cm

Garnet (silicate)

Hardness 6.5-7.5, not scratched by steel

Rhombdodecahedral crystal form, 12 faces each one a rhombus

No cleavage

Red/brown or green in colour

Almandine Garnet, Peru

2cm

Chlorite (silicate)Hardness 2.0,

scratched by fingernail

Perfect basal (parallel) cleavage

Greenish colour

Feels greasy when rubbed between

the fingers

Alteration product from amphiboles,

pyroxenes and micasChlorite, Val Di Vizze, Italy

1cm

Calcite (carbonate)

Hardness 3, just scratched by a copper coin

Perfect rhombohedral cleavage, 3 planes

intersect at 60°/120° to give cleavage rhombs

Effervesces and gives off carbon dioxide when

dilute hydrochloric acid is applied

1cm

Fluorite (halide)

Hardness 4, scratched easily by steel but not

by a copper coin

Perfect octahedral cleavage, cubic crystals

have the corners missing at a 45° angle

Fluoresces in ultra violet light

Commonly purple, green or yellow in colour

1cm

Halite or Rock Salt (halide)

Hardness 2.0-2.5, scratched by a

fingernail

Perfect cubic cleavage, 3 planes intersecting at 90°

Tastes salty when put on the tongue

Halite, Neuhof, Germany

2cm

Gypsum (sulphate)

Hardness 1.5 -2.0, easily scratched by a fingernail

Perfect basal (parallel) cleavage

Often fibrous in appearance (satin spar)

Arrow head/fish tail twinned crystals common

2cm

Barytes/Barite (sulphate)

Hardness 3.0-3.5, barely scratched by a

copper coin

Dense for a non-metallic mineral (4.5)

Often shows perfect basal (parallel)

cleavage, occasionally displays 2 cleavages

Commonly shows bladed crystal 2cm

Chalcopyrite (sulphide)

Hardness 4, not scratched by a

copper coin

Black streak with gold strands within it

Metallic lustre

Greenish gold colour

Tarnishes to peacock colours1cm

Iron Pyrite/Pyrite (sulphide)

Greenish black streak

Hardness 6.0, barely scratched with steel

Metallic lustre

Brassy gold colour

Cubic crystals show striated faces

Strikes fire (sparks) with steel

1cm

Galena (sulphide)

Perfect cubic cleavage, 3 planes

intersect at 90°

Hardness 2.5, easily scratched by a

copper coin

Lead grey streak

Very dense (7.5)

1cm

Haematite (oxide)

Hardness 5.5-6.5, barely scratched by

steel

Cherry red streak

Metallic lustre

Often occurs as kidney shaped masses with a fibrous internal

structure 1cm

Identify this mineral 1

90°

Just scratched by steel

1cm

Identify this mineral 2

Greenish black streak, barely scratched by steel

1cm

Identify this mineral 3

Not scratched by steel, no cleavage

2cm

Identify this mineral 4

Scratched by steel but not by a copper coin

Cubic crystals with edges truncated at 45°

2cm

Identify this mineral 52cm

Not scratched by steel, crystal has 12 faces

Identify this mineral 62cm

Barely scratched by steel, crystals often show simple twins

Cleavage traces

90°

Identify this mineral 7

Feels dense, barely scratched by a copper coin

2cm

Identify this mineral 8

Just scratched by fingernail

1cm1cm

Cleavage directions

Identify this mineral 9

Cleavage traces

120°60°

Just scratched by steel

2cm

Identify this mineral 10

Not scratched by steel

2cm

Identify this mineral 11

2cm

90°

Cleavage traces

Barely scratched by steel, crystals often show multiple twins

Identify this mineral 12Cleavage

traces

2cm

Scratched by a copper coin

Identify this mineral 13

Barely scratched by steel, cherry red streak

2cm

Identify this mineral 14

Can be just scratched by a fingernail

1cm

Identify this mineral 15

Not scratched by steel, needle-like crystals

5mm

Identify this mineral 16

Scratched by a fingernail, fibrous/flaky, feels greasy

1cm

Name this mineral 17

Scratched easily by steel but not by a copper coin, black streak with gold strands

2cm

Name this mineral 181cm

Very dense, scratched by a copper coin, grey streak

Name this mineral 191cm

Reacts with acid, barely scratched by a copper coin, 3 cleavages

Name this mineral 20

1cm

Scratched easily by a fingernail, one plane of cleavage

Cleavage traces

Name this mineral - Answers

1. Augite

2. Iron Pyrite

3. Olivine

4. Fluorite

5. Garnet

6. Orthoclase

7. Barytes

8. Halite

9. Hornblende

10.Quartz

11. Plagioclase

12. Biotite

13. Haematite

14. Muscovite

15. Chiastolite

16. Chlorite

17. Chalcopyrite

18. Galena

19. Calcite

20. Gypsum